gh-72327: Suggest using system terminal for pip install in PyREPL (#136328)

Users new to Python packaging often try to use pip from the REPL only to
be met with a confusing SyntaxError. If this happens, guide the user to
use a system terminal instead to invoke pip.

Closes #72327

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Co-authored-by: Tom Viner <tom@viner.tv>
Co-authored-by: Brian Schubert <brianm.schubert@gmail.com>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>